mine

Oviposition in the underside of the midrib or a thick lateral vein; later a large scar is visible there. Initially the larva tunnels in the midrib or vein, that inflates and disfigures somewhat as a result. Then the larva starts a corridor in the leaf blade, quite narrow at first, but strongly widening as the larva approaches the leaf margin or leaf tip. The mine is reddish brown in colour. The mature larva makes itself a dark brown globular cocoon in the mine and pupates there.

Because the mine is made at a time that the leaf still is unfolding, the leaf becomes permanently rumpled. In the course of the summer the mine erodes away, but the combination of the oviposition scar, the swollen midrib and the frayed leave missing a large part of its distal half remains unmistakable (lower picture).

synonyms

notes

According to Hering (1957a) the species is very common throughout Europe, and this is confirmed for the Netherlands by van Frankenhuyzen a.o. (1982a); in my experience during the last decade is rather uncommon in the Netherlands. Also in the UK the species is fairly scarce (Morris, 1993a)
It has long be assumed that O. testaceus and O. calceatus were one and the same species. This has definitely been refuted by Košťál & Caldara.